1. Field of the Invention
The present invention is generally related to monolithic microwave/millimeter waveguide devices and more particularly to packaging waveguide-to-microstrip transitions for microwave/millimeter waveguide devices.
2. Discussion
In the past, several waveguide-to-microstrip design methodologies have been proposed in an effort to introduce an efficient transition from waveguide to microstrip. The need for such a transition is prompted by the numerous applications it has in present mm-wave (mmW) and microwave/millimeter wave integrated circuit (MMIC) technologies. The increased use of low-cost MMIC components such as low-noise and power amplifiers, in both military and commercial systems continues to drive the search for more affordable and package-integrable transitions.
The current method of signal reception and power transmission within the mmW system is the rectangular waveguide which has a relatively low insertion loss and high power handling capability. In order to keep the overall package cost to a minimum, there is a need for a transition which is mechanically simple and easily integrated into the housing while maintaining an acceptable level of performance.
Current designs have used transitions which were based on stepped ridged waveguides as discussed, for example, in: S. S. Moochalla and C. An, "Ridge Waveguide Used in Microstrip Transition", Microwaves and RF, March 1984; and W. Menzel and A. Klaassen, "On the Transition from Ridged Waveguide to Microstrip", Proc. 19th European Microwave Conf., pp. 1265-1269, 1989. Other designs used antipodal finlines which were discussed, for example, in: L. J. Lavedan, "Design of Waveguide-to-Microstrip Transitions Specially Suited to Millimeter-Wave Applications", Electronic Letters, vol. 13, No. 20, pp. 604-605, September 1997.
Moreover, current designs have used probe coupling which was discussed, for example, in: T. Q. Ho and Y. Shih, "Spectral-Domain Analysis of E-Plane Waveguide to Microstrip Transitions", IEEE Trans. Microwave Theory and Tech., vol. 37, pp. 388-392, February 1989; and D. I. Stones, "Analysis of a Novel Microstrip-to-Waveguide Transition/Combiner", IEEE MTT-S Int'l Symposium Digest, San Diego, Calif., vol. 1, pp. 217-220, 1994.
These current designs suffer from such disadvantages as varying degrees of mechanical complexity. Some of the current transitions are bulky and use several independent pieces that must be assembled in various steps. Additionally, they may require more than one substrate material with multilevel conductors and high-tolerance machining of background housing components such as waveguide steps/tapers, or precise positioning of a backshort. Such precise positioning requirements produce extensive bench tuning after fabrication. Also, current designs require a separate waveguide window and several hermetic sealing process steps to achieve hermetic sealing of the component. These disadvantages render current designs expensive and difficult to integrate into the package.